1. Field of the Invention
The present invention relates to novel, homogeneous sugar-inorganic hybrid composites made from sugar and inorganic substance. Specifically, the invention relates to a sugar-inorganic hybrid composite suitable for recycling utilization, that is, the composite has biodegradability and the degraded product thereof can be used again as a raw-material for sugar-inorganic hybrid production.
2. Related Background Art
Recently, the global environmental pollution has become conspicuous, and environmental consideration is required for not only industrial wastes but also domestic wastes. Plastic resins used as industrial materials are no exception, and research and development are actively carried out to obtain new materials to lessen environmental burden.
On the other hand, certain decomposition products obtained by decomposing resin into lower molecules by thermal decomposition or chemical decomposition may be reused as a raw material for the resin production. For example, polystyrene is decomposed into styrene monomers and dimers by catalytic cracking using a solid catalyst to supply a raw material for polystyrene production. Also polypropylene may be extracted as oil by catalytic cracking.
However, since ordinary resin composites including above-mentioned resins are utilized in wide areas in many ways as various products or parts, it is impossible to recover all of them and collection and sorting of them costs much. Even with collected resins, those not sortable must be disposed by landfill or incineration as wastes.
Incineration will trigger global warming by carbon dioxide discharge, or environmental pollution by toxic gas discharge. On the other hand, most of resin composites will remain intact underground for a long time by landfill.
From such a background, necessity for biodegradable plastics has been growing.
Biodegradable plastic composites are roughly classified into three, i.e., microbial products, natural products of plant origin, and synthetic compounds.
In particular, natural products of plant origin are useful, since the source itself is harmless and biodegradable. Useful natural products include collagen, gelatin, starch, cellulose, and chitosan which can be used as a single material. Further, there are modified natural products such as mixture of starch and modified polyvinyl alcohol, chemically modified cellulose such as cellulose esters, composites of cellulose and chitosan, but the part strength, especially water resistance, is not sufficient when natural products are merely mixed or compounded.
Thus, there are several attempts to make organic-inorganic hybrids maintaining good biodegradability of natural sugars and providing sufficient part strength. As one attempt to use sugar as the organic material, for example, Japanese Patent Application Laid-Open No. 7-309972 discloses a biodegradable moldable composite that comprises a polysaccharide, a metal compound that can bind chemically with hydroxyl groups of the sugar, and a solvent. This method, however, has a problem that the sugar content is low since most of the sugars used therein are water-soluble polysaccharides having poor compatibility with the metal compounds. Japanese Patent Application Laid-Open No. 5-310431 discloses a method to disperse a sugar derivative having urethane bonds, urea bonds, or amide bonds in an inorganic oxide matrix in order to increase the sugar content in the complex. This method, however, needs to synthesize such sugar derivatives having certain bonds by reacting sugar with isopropyl isocyanate etc.
Under such circumstances, future resin composites are strongly required to have excellent biodegradability as well as strength and cost performance comparable with resin composites of general purpose. Usually biodegradable resin composites (Japanese Patent Application Laid-Open No. 5-287043) are disposed by landfill, and seldom recycled. However, it is very important to actively decompose resin and use the decomposition product efficiently. As described above, the degradation product is resins are reused but many degradation products cannot be reused and utilization rate is low. Thus development of resin composites enabling more effective reutilization of decomposition product is expected.
An object of the present invention is to provide sugar-inorganic material composites which can be easily decomposed to give decomposition products polymerable again and of which biodegradability is excellent when disposed by landfill because of the higher sugar content than the conventional resins.
According to the present invention, there is provided a sugar-inorganic hybrid composite wherein a sugar or sugar derivative is evenly dispersed in an inorganic oxide matrix.
The sugar or sugar derivative is preferably a polysaccharide or derivatives thereof soluble in an organic solvent.
The sugar or sugar derivative is preferably cellulose, a cellulose derivative, or chitosan.
The cellulose derivative is preferably a cellulose ester.
The cellulose ester is preferably selected from the group consisting of cellulose acetate, cellulose acetate butyrate, cellulose propionate, benzyl cellulose, cellulose sulfate, or cellulose nitrate.
The inorganic oxide matrix is preferably one or more matrixes selected from the group consisting of silica gel, titanium oxide, aluminum oxides and magnesium oxide.
The novel sugar-inorganic hybrid composite of the invention is a uniform and transparent material made of a sugar and an inorganic substance. This novel sugar-inorganic hybrid composite has biodegradability and gives degradation products which can be used again as raw materials for producing sugar-inorganic hybrid composite.
In addition, the hybrid composites of the invention can be provided at a low cost, since cheap raw materials can be used for production.